Different methodologies may provide different assessments of the prevalence of autism spectrum disorders (ASDs), researchers say.

Action Points

Explain that different methodologies may provide different assessments of the prevalence of autism spectrum disorders (ASDs), with a prevalence of 2.64% in a study of kids ages 7 to 12 in Korea.

Note that the screening process consisted of parents and/or teachers completing an autism questionnaire (the Autism Spectrum Screening Questionnaire [ASSQ]), followed by a confirmatory diagnostic evaluation for those who screened positive.

Different methodologies may provide different assessments of the prevalence of autism spectrum disorders (ASDs), researchers say.

In one South Korean community, analyses done based on surveys of school populations revealed an astonishingly higher prevalence -- 2.64% of kids ages 7 to 12 -- than previous estimates in the developed world, Young Shin Kim, MD, PhD, of Yale, and colleagues reported in the American Journal of Psychiatry.

That rate translates to one in 38 children having an ASD -- far greater than the one in 110 commonly cited by the CDC.

The findings suggest that "rigorous screening and comprehensive population coverage are necessary to produce more accurate ASD prevalence estimates and underscore the need for better detection, assessment, and services," they wrote.

Case identification methods are important when estimating ASD prevalence, Kim and colleagues said, noting that CDC estimates vary from 0.75% when based solely on health records to 1% when based on education and health records combined.

In addition, the prevalence of ASDs in South Korea has not yet been estimated.

To get that estimate and to test the new methodology, the researchers assessed one community in South Korea -- the Ilsan district of Goyang City, a "stable, residential community near Seoul," with a total of 55,266 children ages 7 to 12.

They divided the cohorts into two samples: one representative of the general population, and the other a "high-probability" group focused on special education students.

Of 44 schools asked to participate, 33 agreed, for a total of 36,592 kids in the general population group and 294 in the disability group.

Response rates were 63% of the normal group and 35% of the special education group, making for a total of 23,337 children -- 23,234 and 103, respectively.

The screening process was twofold: Parents and/or teachers completed an autism questionnaire (the Autism Spectrum Screening Questionnaire [ASSQ]), followed by a confirmatory diagnostic evaluation for those who screened positive.

Of the 1,214 children who were positive for ASDs, 286 completed the testing and 201 were confirmed to have the disease, yielding a crude prevalence for any ASD of 0.36%.

After statistical adjustment to account for those who didn't participate, ASD prevalence was estimated to be 2.64%, the researchers said.

The general population group accounted for 1.89% while the high-probability group explained the remaining 0.75%.

"Of course, if you screen all children, the number will be higher," Susan Hyman, MD, from the University of Rochester School of Medicine in New York, told MedPage Today in an email. Hyman, who is chief of neurodevelopmental pediatrics, was not involved in the study.

She added that it's particularly relevant for patients who have clinical profiles of ASDs "but because of environmental supports, or other factors related to personal resilience, are not functionally impacted in a fashion that clinical services are sought."

The authors acknowledged other limitations of their study, including funding from Autism Speaks, the autism advocacy organization. Also, the survey had an overall low response rate (63%) and parents of children with ASDs may have accounted for a greater proportion of the study population. Parents whose children did not have ASDs and were not in need of healthcare services may have been less inclined to respond.

Indeed, Kim and colleagues note that it's "possible that our calculations overestimate prevalence as a result of a less-than-optimal participation rate in our general population sample."

"It could be argued that in this cultural context, with few services for children with developmental disorders, parents of children with serious but unrecognized developmental problems would be more likely to participate in research than parents of unaffected children," they said.

The researchers also found a much lower male-to-female ratio than in previous estimates, at 2.5-to-1 in the general sample. That of the disability sample was higher, at 5-to-1, but still lower than normal, the researchers said.

Additionally, they found that more of the children with ASDs in the general sample had superior IQs compared with those in the special education group (12% versus 7%), while more of those in the latter group had intellectual disability (59% versus 16%).

The study was supported by a pilot research grant from Autism Speaks.

It was also supported by grants from the Children's Brain Research Foundation, NIMH career awards, the George Washington University Institute for Ethnographic Research, the Jean Young and Walden W. Shaw Foundation, the Daniel X. and Mary Freedman Foundation, and the Dukyoung Foundation.

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